The aim of this study is to measure an iron bioavailability during a resting and an exercise phase lasting approx. 14 days with training sessions on alternate days. Subjects will participate in both restign and exercising protocols and act as their own controls during the study. Iron bioavailability will be measured via the incorporation of stable isotopic labels 14 days after administration. To control for changes in blood volume during the course of the study, blood volume of the participating subjects will be measured before and after the exercise phase with the CO-rebreathing method.